Electro-oxidation of amino-functionalized multiwalled carbon nanotubes

Abstract

We report the electrochemistry of amino-functionalized multiwalled carbon nanotubes (MWCNTs-NH₂) in the pH range from 0.3 to 6.4 using quantitative cyclic voltammetry (CV) and single entity electrochemistry measurements, making comparison with non-functionalized MWCNTs. CV showed the latter to both catalyze the solvent (water) decomposition and to undergo irreversible electro-oxidation forming oxygen containing surface functionality. The MWCNTs-NH₂ additionally undergo an irreversible oxidation to an extent which is dependent on the pH of the solution, reflecting the variable amount of deprotonated amino groups present as a function of pH. Nano-impact experiments conducted at the single particle level confirmed the oxidation of both types of MWCNTs, showing agreement with the CV. The pK_a of the amino groups in MWCNTs was determined via both electrochemical methods giving consistent values of ca. 2.5.